Transformer coils with dielectric insertion



Oct. 6, 1970 G. A. KOCH 3,533,037

TRANSFORMER COILS WITH DIELECTRIC INSERTION Filed Aug. 50, 1968 FIGZ mummngimgmmg:mug Ulllllllllllllll F|G4 I4 44 2s 6 36 f r f 34 38 'l Ill I I [I [FIGS INVENTOR I GEORGE A.KOCH 3 2 BY ATTORNEXS,

3,533,037 TRANSFORMER COILS WITH DIELECTRIC INSERTION George A. Koch, Quincy, Ill., assignor to Motorola, Inc., Franklin Park, Ill., a corporation of Illinois Filed Aug. 30, 1968, Ser. No. 756,661 Int. Cl. H01f 27/32 US. Cl. 336--206 Claims ABSTRACT OF THE DISCLOSURE A dielectric insertion for reducing arcing between the first and second windings of a bobbin-wound coil that includes an elastic strip of dielectric material having adhesive on both sides. A rigid dielectric film is laminated to the adhesive on one side of the material and has serrations at the edges thereof. The insertion is wound around the first winding and fastened thereto by the adhesive on the other side of the elastic material. The serrations of the rigid film guide the elastic material as it is being applied to the winding and form fillets about the core flanges. These fillets of dielectric material extend the path of the electric field between the two coil windings to reduce arcing therebetween.

BACKGROUND OF THE INVENTION This invention pertains to electric transformers and more particularly to the reduction of arcing between first and second windings of a bobbin-wound coil.

In general, random wound, bobbin coils experience voltage breakdown and arcing at potentials greater than 1500 volts AC. It has been proposed to increase the alternating current potentials which can be present on such coils by placing an elastic dielectric tape between the first and second windings of the coil, which tape forms fillets on the bobbin flanges. The fillets extend the di electric on the flanges between the first and second windings of the transformer increasing the path of the electric field between the windings to reduce arc-over. The process of applying the tape, however, to form symmetrical fillets about the flanges has been extremely time consuming because for the most part it must be done by hand.

SUMMARY OF THE INVENTION It is an object of this invention to provide improved means for reducing arc-over between first and second windings of a transformer.

It is another object of this invention to provide an improved dielectric insertion between the first and Second windings of a random wound, bobbin coil to prevent areover between the windings thereby increasing the alternating current voltage which can be applied to the coil.

In one embodiment of this invention, an insulated coil support for a transformer includes a core intermediate first and second flange portions. A first winding is wound about the core. A dielectric strip having an adhesive on one side thereof and a rigid backing film on the other side is wrapped around the first winding. The rigid backing film is serrated at the edges thereof over the entire length of the strip. As the dielectric strip is wound about the first winding, the serrated edges of the film acts to guide the strip to form fillets about the first and second flanges. These fillets of dielectric material extend the path of the electric field between the first and second windings of the transformer thereby reducing the arcing between these windings.

DESCRIPTION OF THE DRAWING FIG. 1 is a side elevation view of a random wound nited States Patent O M 3,533,037 Patented Oct. 6, 1970 bobbin coil in accordance with the principles of this invention;

FIG. 2 is a plan view of a dielectric insertion to be used with the device of FIG. 1, in accordance with the principles of this invention;

FIG. 3 is an enlarged cross-section view in elevation along the lines 33 of FIG. 2;

FIG. 4 is an enlarged cross-section of a portion of the device of FIG. 1 showing first and second coils wound thereon; and

FIG. 5 is an enlarged cross-section view of a portion of the device of FIG. 1 taken along the line 55.

DETAILED DESCRIPTION Referring to the figures of the drawing, FIG. 1, shows a coil bobbin 10 made of a dielectric material such as plastic and which includes an insulated core 12 (FIG. 5 integral with and intermediate first and second flanges 14 and 16. Integral with the flange portion 16 are first and second shelf portions 18 and 20, which carry the terminals 22, 22a and connectors 24 and 24a. Wound about the insulated core 12 is a first or primary winding 26 of a transformer (FIG. 5).

As is common in random wound bobbin coils such as described here, an insulating strip is secured around the winding 26, and the secondary winding 28 (FIG. 4) is then wound on the bobbin about the strip. The strip acts to insulate the secondary winding from the primary winding to prevent arcing therebetween. This arrangement is acceptable when the voltage on the transformer is under 1500 volts AC. However, until now, a problem has existed when the alternating voltage on the transformer exceeds 1500 volts. At this point, there is a voltage breakdown and arcing occurs between the windings.

A dielectric insertion has been conceived in accordance with this invention which operates to prohibit this arcing between the winding at applied voltages greater than 1500 volts AC. Referrng to FIGS. 2 and 3, there is shown a dielectric insertion 30 comprising a strip of elastic dielectric tape 32 made of a polyester material such as Mylar, which is a registered trademark of the Du Pont Company. The elastic tape 32 has adhesive layers 34 and 36 on each side thereof. Laminated to the top adhesive layer 34 is a rigid backing or polyester film 38. The edges 40 and 42 of the film 38 are serrated such as at 44 over the entire length of the strip 30.

In practice (FIG. 4), the first or secondary winding 26 is wound about the core 12 of the bobbin 10. Subsequently, dielectric insertion 30 is wound about the winding 26. As can be seen in FIG. 2, the width of the film 38 is greater than the Width of the dielectric elastic material 3 2 and is also greater than the distance between the flanges 14 and 16. Therefore, as the insertion 30 is wrapped around the coil 26, the serrated portions 44 along the edges 40 and 42 of the tape form an even fillet about the flanges 14 and 16 of the bobbin 10. Because the width of the elastic dielectric material 32 is only silghtly less than that of the film, the serrated portion 44 acts to guide the dielectric tape 32 about the flange portions 14 and 16 to form an even fillet 46 (FIG. 4) about each of the flanges 14 and 16 (FIG. 1). The fillet 46 in effect extends the path of the electric field, shown by the arrows at 48 (FIG. 4), between winding 26 and the winding 28. By the time the electric field reaches the end of the fillet 46, the potential thereof has been greatly reduced, resulting in an increase in the amount of alternating voltage that can be impressed upon the windings of the transformer without causing arcing therebetween. In one operating installation, for instance, voltages as great as 2,000 volts AC were impressed on the transformer without causing arcing between the primary and secondary windings.

What has been described, therefore, is an improved random-wound, bobbin coil which permits alternating current voltages in excess of 1500 volts to be present without experiencing arc-over between the primary and secondary windings on the bobbin.

I claim:

1. A transformer having an insulated coil support comprising a core intermediate first and second flange portions, including in combination a first winding wound about the core, dielectric strip means having substantially uninterrupted edges having an adhesive on one side thereof and rigid backing means on the other side, said rigid backing means being serrated at the edges thereof over the length of the strip, said dielectric strip means being wrapped about said first winding with said serrated edges of said backing means guiding said strip means to form a fillet about the first and second flange portions and said. adhesive adhering said strip means thereto, and a second winding wound on said dielectric strip means over said first winding with said fillet reducing the arcing between said first and second windings.

2. The transformer of claim 1 wherein said dielectric strip means is wider than the distance between the first and second flange portions and comprises a strip of elastic dielectric material having adhesive on both sides thereof, and a rigid dielectric film laminated to one side of said strip to form said rigid backing means, said rigid film having serrated edges.

3. The transformer of claim 1 wherein said second winding is wound on said dielectric strip means over said first winding and between said flanges, said fillets extending beyond said second winding to increase the path of the electric field between said first and second windings thereby reducing arcing therebetween.

4. A dielectric insertion positioned between first and second windings of a transformer wound between end flanges on the core of a coil bobbin for reducing arcing therebetween, the insertion including in combination, a strip of dielectric material having substantially uninterrupted edges having adhesive on both sides thereof, a rigid film laminated to the adhesive on one side of said material, said rigid film having serrations at the edges thereof, said dielectric material being fixed about the first winding of the transformer by said adhesive on the side of the same opposite said one side, and said serrated edges of said rigid film guiding said dielectric material with the same being fixed about the first winding to form a fillet of said dielectric material about each flanged portion of the bobbin to increase the path of travel of the electric field between the first and second windings thereby reducing arcing therebetween.

5. The dielectric insertion of claim 4 wherein the width of said dielectric material and said rigid backing laminated thereto is greater than the distance between the flange portions of the bobbin.

References Cited UNITED STATES PATENTS 2,435,093 1/1948 Mitschrich 336-206 2,503,483 4/ 1950 Hartmann 336-229 2,976,504 3/1961 Christoffel 336-185 3,203,823 8/1965 Grimes 161-167 FOREIGN PATENTS 100,091 12/ 1961 Netherlands.

ELLIOT A. GOLDBERG, Primary Examiner 

